/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.connector.file.src.util;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.connector.file.src.reader.BulkFormat;

import javax.annotation.Nullable;

/**
 * A simple {@link BulkFormat.RecordIterator} that returns a single value.
 * The iterator is mutable to support object reuse and supports recycling.
 *
 * @param <E> The type of the record returned by the iterator.
 */
@PublicEvolving
public final class SingletonResultIterator<E> extends RecyclableIterator<E> implements BulkFormat.RecordIterator<E> {

	@Nullable
	private RecordAndPosition<E> element;

	private final MutableRecordAndPosition<E> recordAndPosition;

	public SingletonResultIterator() {
		this(null);
	}

	public SingletonResultIterator(@Nullable Runnable recycler) {
		super(recycler);
		this.recordAndPosition = new MutableRecordAndPosition<>();
	}

	// -------------------------------------------------------------------------
	//  Setting
	// -------------------------------------------------------------------------

	/**
	 * Sets the single record to be returned by this iterator.
	 * The offset and records-to-skip count will be used as provided here for the returned
	 * {@link RecordAndPosition}, meaning they need to point to AFTER this specific record
	 * (because a checkpoint taken after the record was processed needs to resume from after this record).
	 */
	public void set(final E element, final long offset, final long skipCount) {
		this.recordAndPosition.set(element, offset, skipCount);
		this.element = this.recordAndPosition;
	}

	// -------------------------------------------------------------------------
	//  Result Iterator Methods
	// -------------------------------------------------------------------------

	@Nullable
	@Override
	public RecordAndPosition<E> next() {
		final RecordAndPosition<E> next = this.element;
		this.element = null;
		return next;
	}
}
